Sheet finishing apparatus and sheet finishing method

ABSTRACT

A sheet finishing apparatus includes an outer wall having a discharge port of sheets; a movable tray on which the sheets discharged from the discharge port are stacked, the movable tray vertically moving along the outer wall according to a stack amount of the sheets; a curl sensor that detects a curled state of the sheets before the sheets are discharged from the discharge port; and a control unit that controls at least one of a discharge speed of the sheets and a position of the movable tray according to the detected curled state of the sheets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from: U.S. provisional applications 61/311,261 filed on Mar. 5, 2010, 61/311,263 filed on Mar. 5, 2010, and 61/311,265 filed on Mar. 5, 2010, the entire contents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a sheet finishing apparatus and a sheet finishing method.

BACKGROUND

Up to now, a sheet finishing apparatus has been known which is located downstream of an image forming apparatus such as a copying machine, a printer, or a multi-functional peripheral (MFP), and conducts post-processing such as sorting or stapling on a printed sheet.

The sheet finishing apparatus of this type may be equipped with a fixed tray and a movable tray as a tray onto which sheets are discharged and stacked. If a relatively small number of sheets are discharged, the fixed tray is normally selected. On the other hand, if a large number of sheets, for example, 1000 or more sheets are discharged, the movable tray is selected. Even when sorting or stapling is conducted on a bundle of sheets, the movable tray is also selected.

The movable tray is configured to move vertically according to the number of sheets for the purpose of stacking a large number of sheets thereon. The movable tray receives the sheets at a higher position when the number of sheets is smaller, and moves down with an increase in the number of sheets.

A mounting surface of the movable tray is tilted at a given tilt angle so that a front end side of each sheet becomes higher in position than a rear end side thereof. With the tilted mounting surface of the movable tray, the mounted sheets are prevented from dropping outside the movable tray. The rear end of the sheet that has slid along the tilted mounting surface is abutted against an outer wall surface of the sheet finishing apparatus, and stops.

Both ends of the sheet discharged from a discharge port of the sheet finishing apparatus into the movable tray may be curled upward or downward. In the present specification, the sheet both ends of which are curled upward is called “upward curled sheet” and the sheet both ends of which are curled downward is called “downward curled sheet”.

When a large number of downward curled sheets are stacked on the movable tray, the front ends of the stacked sheets are curved downward. For that reason, newly discharged sheets slide along the downward curved front side of the stacked sheets even though the mounting surface of the movable tray is tilted. As a result, the newly discharged sheets may drop ahead of the movable tray.

On the other hand, if a large number of upward curled sheets are stacked on the movable tray, the front ends of the stacked sheets are curved upward. For that reason, there may occur a so-called “buckling phenomenon” that an end of each newly discharged sheet hit a wall of upward curved front sides of the stacked sheets, and the discharged sheet is curved in the middle such that the front end of the sheet bends down. Also, when the discharged sheet stops in front of a normal stacked position, a rear end of the sheet does not drop down to a position of an uppermost stacked sheet, resulting in a phenomenon that is so-called “rear end residual”. The rear end residual is directed to an incomplete sheet stacking phenomenon in which the rear end of the sheet is pulled up to an outer wall surface of the sheet finishing apparatus, and the sheet is curved. When the rear end residual occurs, there occurs a case in which normal discharge is impeded, and not only an alignment property is deteriorated but also the sheets cannot be stacked up to a normal maximum stack amount.

Under the circumstances, a sheet finishing apparatus is desired, which can prevent drop of the sheets and a reduction in the maximum stack amount, and also stack the sheets with the excellent alignment property, even if the sheets are curled.

DESCRIPTION OF THE DRAWINGS

In the attached drawings,

FIG. 1 is a perspective view illustrating an external example of a sheet finishing apparatus and an image forming apparatus according to an embodiment;

FIG. 2 is an enlarged view illustrating an upper portion of the sheet finishing apparatus;

FIG. 3 is a cross-sectional view illustrating a configuration example of the sheet finishing apparatus;

FIG. 4 is a diagram describing a positional relationship between a standby tray and a processing tray;

FIG. 5 is a diagram illustrating a detailed configuration example of the processing tray;

FIG. 6 is a diagram illustrating a flow of sheets when the sheets are discharged to a movable tray through the standby tray;

FIG. 7 is a diagram illustrating a flow of the sheets when the sheets are discharged to the movable tray through the processing tray;

FIGS. 8A to 8B are diagrams describing operation of dropping the sheets on the processing tray from the standby tray;

FIGS. 9A and 9B are diagrams describing vertical movement of a shutter;

FIG. 10 is a diagram describing a configuration example of a neighborhood of an upper portion of the shutter;

FIG. 11 is a schematic perspective view describing a drive mechanism of the movable tray;

FIGS. 12A and 12B are diagrams describing a problem arising when a downward curled sheet is stacked on the movable tray;

FIGS. 13A and 13B are diagrams describing a problem arising when an upward curled sheet is stacked on the movable tray;

FIG. 14 is a functional block diagram of the sheet finishing apparatus related to control of a discharge speed and a movable tray position;

FIGS. 15A to 15C are diagrams describing an operation principle of a sheet curled state detection by a curl sensor;

FIG. 16 is a flowchart showing a processing example of the control of the discharge speed and the movable tray position in the sheet finishing apparatus according to a first embodiment;

FIGS. 17A and 17B are diagrams describing the control of the movable tray position to the downward curled sheets in the first embodiment;

FIGS. 18A and 18B are diagrams describing the control of the movable tray position to the upward curled sheets in the first embodiment;

FIG. 19 is a flowchart showing a processing example of the control of the movable tray position in a sheet finishing apparatus in a second embodiment;

FIGS. 20A and 20B are diagrams describing the control of the movable tray position to the downward curled sheets in the second embodiment;

FIG. 21 is a diagram describing a rear end residual phenomenon occurring in the upward curled sheets;

FIGS. 22A and 22B are diagrams describing the control of the movable tray position to the upward curled sheets in the second embodiment;

FIGS. 23A to 23F are diagrams describing a concept of discharge speed control in a sheet finishing apparatus according to a third embodiment; and

FIG. 24 is a flowchart showing a processing example of the discharge speed control in the sheet finishing apparatus according to the third embodiment.

DETAILED DESCRIPTION

Embodiments of a sheet finishing apparatus and an image forming apparatus will be described with reference to the accompanying drawings.

A sheet finishing apparatus according to this embodiment includes: an outer wall having a discharge port of sheets; a movable tray on which the sheets discharged from the discharge port are stacked, the movable tray vertically moving along the outer wall according to a stack amount of the sheets; a curl sensor that detects a curled state of the sheets before the sheets are discharged from the discharge port; and a control unit that controls at least one of a discharge speed of the sheets and a position of the movable tray according to the detected curled state of the sheets.

(1) Configuration

FIG. 1 is an external perspective view illustrating a basic configuration example of an image forming apparatus 100 with a sheet finishing apparatus 1 according to a first embodiment. The image forming apparatus 100 includes an image forming apparatus main body 2 and the sheet finishing apparatus 1 arranged adjacent to the main body 2.

The main body 2 includes a scanner 3 that reads an original document, and a printer 4 that prints an image read by the scanner 3 on a sheet.

The sheet finishing apparatus 1 includes a fixed tray 10 to which the sheets printed by the main body 2 are discharged, and on which the sheets are stacked, and a movable tray 11 that moves vertically as indicated by an arrow, and on which a large number of print sheets are stacked. The sheet finishing apparatus 1 has a function of sorting a plurality of printed sheets (a bundle of sheets), and a stapling function.

The movable tray 11 moves vertically along an outer wall 50 at a discharge side of the sheet finishing apparatus 1.

FIG. 2 is an enlarged view illustrating an upper portion of the sheet finishing apparatus 1. FIG. 2 is a view taken from the same direction as that in FIG. 1.

As indicated by white arrows in FIG. 2, a direction in which the sheets or the bundle of sheets are discharged is called “discharge side”, a direction in which the main body 2 is located is called “main body side”, a right side when the main body side is viewed from the discharge side is called “front side”, and a left side is called “rear side”.

A discharge port 13 is disposed between the fixed tray 10 and the movable tray 11, and the sheets or the bundle of sheets stacked on the movable tray 11 are discharged from the discharge port 13.

A processing tray 30 is disposed at the back and bottom of the discharge port 13. Lateral alignment plates 38 a and 38 b are disposed at the front side and the rear side of the processing tray 30, respectively. In FIG. 2, only the lateral alignment plate 38 a at the rear side is shown.

FIG. 3 is a cross-sectional view taken from the front side, schematically illustrating a main internal configuration of the sheet finishing apparatus 1.

Input rollers 21 are located at a position opposite to output rollers 101 of the main body 2, and a gate flap 22 is disposed downstream of the input rollers 21. Fixed tray rollers 23 are disposed above the gate flap 22. A downward curved transport guide plate 24 and transport rollers 25 are disposed below the gate flap 22, and a standby tray 26 is disposed beyond the transport rollers 25.

The standby tray 26 is tilted such that a height of an end thereof at the main body side is lower than that at the discharge side, as illustrated in FIG. 3. A buffer roller 27 is disposed in the vicinity of a front end of the standby tray 26 at the discharge side. On the other hand, a paddle 28 is disposed in the vicinity of the standby tray 26 at the main body side.

FIG. 4 is an external perspective view schematically illustrating a structure of the standby tray 26. In FIG. 4, the standby tray 26 is hatched, and the processing tray 30 disposed below the standby tray 26 is indicated by broken lines. The standby tray 26 includes two components of a standby tray 26 a at the rear side and a standby tray 26 b at the front side. The standby tray 26 can be opened and closed in a front and rear direction, as will be described later, with a drive mechanism not shown.

The standby tray 26 is equipped with a sensor main body 200 of a curl sensor 202. The operation of the curl sensor 202 and the sensor main body 200 will be described later.

As shown in FIG. 3, the processing tray 30 is disposed below the standby tray 26. Like the standby tray 26, the processing tray 30 is also tilted such that a height of an end thereof at the main body side is lower than that at the discharge side. A shutter 41 is disposed between the processing tray 30 and the movable tray 11, along the outer wall 50 at the discharge side of the sheet finishing apparatus 1. The shutter 41 is movable vertically, and as will be described later, moves up when the sheet is discharged directly to the movable tray 11 from the standby tray 26, and closes an opening portion between the standby tray 26 and the processing tray 30 in the discharge port 13. A stapler 40 is disposed beyond the processing tray 30 at the main body side.

FIG. 5 is a perspective view illustrating a configuration of the processing tray 30 and a periphery thereof. The processing tray 30 is divided into the two processing trays 30 a and 30 b at the rear side and the front side in the center. Ends of the processing trays 30 a and 30 b at the main body side are provided with rear stoppers 31 a and 31 b, respectively, and ends thereof at the discharge side are provided with four sheet bundle transport rollers 36.

At a divided portion of the processing tray 30, a bundle claw belt 34 and eject belts 32 a, 32 b are arranged adjacent to each other.

A bundle claw 35 is fixed to an outer periphery of the bundle claw belt 34. The bundle claw belt 34 moves the bundle claw 35 from the main body side to the discharge side on a front surface of the processing tray 30, whereas the bundle claw belt 34 consecutively rotates so as to return from the discharge side to the main body side on a rear surface of the processing tray 30.

On the other hand, ejectors 33 a and 33 b are fixed to the outer peripheries of the eject belts 32 a, and 32 b, respectively. The eject belts 32 a, 32 b are coupled with the same drive source as that of the bundle claw belt 34 by an electromagnetic clutch (not shown). The eject belts 32 a, 33 b move the ejectors 33 a and 33 b to a neighborhood of the center portion of the processing tray 30 substantially in synchronism with the movement of the bundle claw 35. When the ejectors 33 a and 33 b transport the rear end of each sheet to the neighborhood of the center portion of the processing tray 30, the bundle claw 35 of the bundle claw belt 34 takes over the transport of the sheet, and the bundle claw 35 pushes out the rear end of the sheet toward the movable tray 11 side. On the other hand, after the transport of the sheet is taken out to the bundle claw 35, the electromagnetic clutch turns off, and the ejectors 33 a and 33 b are returned to a position (home positions of the ejectors 33 a and 33 b) illustrated in FIG. 6 with the help of an elastic force of a spring not shown. In this way, the bundle claw 35 consecutively rotates about the processing tray 30 whereas the ejectors 33 a and 33 b reciprocate on the processing tray 30.

The home positions of the ejectors 33 a and 33 b are at substantially the same positions as those of rear stoppers 31 a and 31 b.

The processing trays 30 a and 30 b are equipped with the lateral alignment plates 38 a and 38 b, respectively. The lateral alignment plates 38 a and 38 b are so configured as to be movable in a rear and front direction with the driven mechanism. One stapler 40 is disposed at the main body side of the processing tray 30. The stapler 40 staples a bundle of sheets printed by the main body 2.

Stack modes of the sheet finishing apparatus 1 are roughly classified into two modes of a simple stack mode and a processing stack mode.

The simple stack mode is an operation mode in which the printed sheet is simply discharged and stacked as it is. In the simple stack mode, a user can select any one of the fixed tray 10 and the movable tray 11 as a tray for discharging and stacking. The movable tray 11 gradually moves down with an increase in the number of stacked sheets, and a large number (for example, 2000 or more) of sheets can be stacked on the movable tray 11. For that reason, when the number of prints is large, the movable tray 11 is selected by the user as a discharge target.

FIG. 6 is a diagram illustrating a flow of sheet in the simple stack mode when the movable tray 11 is selected as the discharge target. When the movable tray 11 is selected, the gate flap 22 guides the sheets from the input rollers 21 toward the transport rollers 25, as illustrated in FIG. 6. A sheet <1> printed by the main body 2 is pulled from the output rollers 101 by the input rollers 21 of the sheet finishing apparatus 1. Thereafter, the sheet <1> moves downward along the gate flap 22, is put on the standby tray 26 once, and goes toward the buffer roller 27 <2>. In this situation, the standby trays 26 a and 26 b are closed (a state of FIG. 8A), and the sheet does not drop on the processing tray 30. Also, the buffer roller 27 rotates in an arrow direction of FIG. 6 while contacting the standby tray 26. Thus, the sheet put on the standby tray 26 is pulled by the buffer roller 27, discharged onto the movable tray 11, and sequentially stacked thereon <3>.

In the simple stack mode when the movable tray 11 is selected, the shutter 41 moves up, and an opening portion between the standby tray 26 and the processing tray 30 in the discharge port 13 is closed. The shutter 41 prevents the sheet discharged to the movable tray 11 or the sheet stacked thereon from returning onto the processing tray 30 through the discharge port 13.

FIG. 7 is a diagram illustrating a flow of the sheets in the processing stack mode. In the processing stack mode, sorting is conducted in such a manner that the sheets or a bundle of sheets are discharged while being alternately offset to the front side and the rear end, and then stacked, and stapling of an edge of the bundle of sheets is conducted at one or two positions. Those sorting and stapling are conducted on the processing tray 30.

After the sheet <1> printed by the main body 2 is pulled from the output rollers 101 by the input rollers 21 of the sheet finishing apparatus 1, the sheet moves downward along the gate flap 22, and is then put on the standby tray 26 temporarily. In this situation, the standby trays 26 a and 26 b are closed as illustrated in FIG. 8A. An interval between the standby trays 26 a and 26 b that are closed is different depending on a sheet size, and a sheet P in any size is received by the standby tray 26 once without dropping directly on the processing tray 30 (FIG. 8B).

Thereafter, the standby trays 26 a and 26 b are opened in the front and rear direction as illustrated in FIG. 8C, and the sheet P drops on the processing tray 30 (FIG. 8D).

A given number of sheets are stacked on the processing tray 30, and a rear edge of a bundle of sheets is pushed against the rear stoppers 31 a and 31 b and the ejectors 33 a and 33 b to perform vertical alignment. Also, the lateral alignment plates 38 a and 38 b are pushed against edges of the bundle of sheets at both sides thereof to perform lateral alignment.

The sorting is conducted by alternately offsetting positions of the lateral alignment at the front side and the rear side for each bundle of sheets to be processed after vertical alignment.

On the other hand, the stapling is conducted by the stapler 40 after the vertical alignment and the lateral alignment are finished.

The bundle of sheets that has been sorted and stabled, are discharged from the processing tray 30, and then sequentially stacked on the movable tray 11. Also, in the simple stack mode, when the movable tray 11 is selected, the sheets are discharged from the standby tray 26, and then sequentially stacked on the movable tray 11.

FIGS. 9A and 9B are schematic diagrams for describing the operation of the shutter 41 in the configuration of a periphery of the movable tray 11. The shutter 41 moves vertically. If the sheets are discharged from the processing tray 30 to the movable tray 11, the shutter 41 waits at a first standby position where the discharge of the sheets is not disturbed, as illustrated in FIG. 9A. On the other hand, if the sheets are discharged directly from the standby tray 26 to the movable tray 11, the shutter 41 moves up to an upper second standby position from the first standby position, as illustrated in FIG. 9B. That is, the shutter 41 that waits at the second standby position prevents the sheets discharged from the standby tray 26, or the sheets on the movable tray 11 from entering the processing tray 30 side. A state in which the shutter 41 waits at the first standby position is called “open state” whereas a state in which the shutter 41 waits at the second standby position is called “close state”.

The shutter 41 has a step 411 on a surface thereof at the movable tray 11 side, as shown in FIG. 9B. The outer wall 50 also has a step 501. The shutter 41 moves vertically along the outer wall 50 of the sheet finishing apparatus 1. When the sheets are discharged from the processing tray 30, the step 411 of the shutter 41 is abutted against the step 501 of the outer wall 50 so that the shutter 41 does not further drop.

In this situation, as illustrated in FIG. 10, the shutter 41 waits at a position where a front end of the shutter 41 is located lower than the sheet stack surfaces of the processing trays 30 a and 30 b. A front end of the shutter 41 is equipped with a sheet height sensor 132 that detects an upper surface of the movable tray 11, or the uppermost surface of the sheets stacked on the movable tray 11. The sheet height sensor 132 may be formed of, for example, a micro-sensor or a micro-actuator.

FIG. 11 is a schematic perspective view illustrating a drive mechanism of the movable tray 11 according to this embodiment.

The movable tray 11 moves vertically by the aid of a drive mechanism 142. The movable tray 11 moves along an outer surface of the shutter 41 in an upper portion of a movable range, and moves along an outer surface of the outer wall 50 in a lower portion of the movable range.

The drive mechanism 142 includes a motor M2, a gear 143, pulleys 144, 145, 154, 155, belts 146, 156, and shafts 147, 157. The motor M2 may be, for example, a DC motor. The pulleys 144 and 145 allow the belt 146 to be wound therearound. Also, the pulleys 154 and 155 allow the belt 156 to be wound therearound. The pulleys 144 and 154 are fitted to the shaft 147. The pulleys 145 and 155 are also fitted to the shaft 157. A power of the motor M2 is transmitted to the shaft 147 through the gear 143. The movable tray 11 is attached to the belts 146 and 156 by means of attaching members 148 and 158. Accordingly, when the motor M2 is driven, the movable tray 11 moves up or down.

The movable tray 11 has a movable-tray position sensor 111 (see also FIG. 14) for detecting a vertical position of the movable tray 11.

(2) Operation on Curled Sheet (First Embodiment)

The sheet discharged from the discharge port 13 of the sheet finishing apparatus 1 to the movable tray 11 may include a downward curled sheet having both ends or one end downward curled, or an upward curled sheet having both ends or one end upward curled.

FIGS. 12A and 12B are diagrams schematically illustrating a problem arising when the downward curled sheets are stacked on the movable tray 11. FIG. 12A is a diagram illustrating a stacked state of uncurled sheets for comparison, and FIG. 12B is a diagram illustrating a state in which a large number of downward curled sheets are stacked on the movable tray 11.

When a large number of downward curled sheets are stacked on the movable tray 11, as illustrated in FIG. 12B, front ends of the stacked sheets are curved downward. For that reason, a newly discharged sheet may slide along the downward curved front portion of the stacked sheets, and drop beyond the movable tray 11 although the stacking surface of the movable tray 11 is tilted.

On the other hand, FIGS. 13A and 13B are diagrams schematically illustrating a problem arising when the upward curled sheet is stacked on the movable tray 11. FIG. 13A is a diagram illustrating a stacked state of uncurled sheets for comparison, and FIG. 13B is a diagram illustrating a state in which a large number of upward curled sheets are stacked on the movable tray 11.

When a large number of upward curled sheets are stacked on the movable tray 11, front ends of the stacked sheets are curved upward. For that reason, there may occur a so-called “sheet buckling phenomenon” in which a front end of a newly discharged sheet hits a wall of upward curved front portions of the stacked sheets, and the discharged sheet is curved in the middle.

In order to address the above problems, a sheet finishing apparatus 1 according to the first embodiment is configured to include a curl sensor 201 and a control unit 204 as illustrated in FIG. 14.

The curl sensor 201 includes, for example, a sensor main body 200 made up of a reflective optical sensor, and a curled state determination unit 202. The sensor main body 200 is disposed, for example, on the standby tray 26 (refer to FIG. 4), and the curled state determination unit 202 detects a curled state of the sheet before the sheet is discharged from the discharge port 13 on the basis of an output signal of the sensor main body 200.

The curled state of the sheet is directed to, for example, a state of the downward curl in which both ends or one end of the sheet is downward curved, a state of the upward curl in which both ends or one end of the sheet is upward curved, or a state in which the sheet is not curled. Also, when the sheet is curled, the curl sensor 201 may further detect the amount of curl of the downward curl or the upward curl.

FIGS. 15A to 15C are diagrams illustrating an example of a concept of the operation of detecting the curled state or the amount of curl of the sheet.

The sensor main body 200 is a reflective optical sensor, and detects a pattern of a change in the reflection intensity from the sheet with time while the sheet passes through a transport path on the standby tray 26.

When the sheet is not curled, as illustrated in FIG. 15A, the reflection intensity monotonically increases at the front end of the sheet, and thereafter becomes a given level. If the sheet is downward curled, as illustrated in FIG. 15B, the reflection intensity precipitously increases at the front end of the sheet, and thereafter slightly decreases to arrive at a given level. On the other hand, if the sheet is upwardly curled, the reflection intensity is small as compared with a case where the sheet is not curled even though the front end of the sheet passes through the transport path, and gradually increases to arrive at a given level.

In this way, the pattern of the change in the reflection intensity with time is different according to the sheet state in which the sheet is downward curled, upward curled, or not curled. Therefore, the curled state of the sheet can be determined on the basis of the change in the reflection intensity with time. Also, because the change in the reflection intensity with time is different depending on the amount of curl, the amount of curl can be detected according a difference in the change in the reflection intensity with time.

The control unit 204 illustrated in FIG. 14 controls at least one of the discharge speed of the sheet and the position of the movable tray 11 on the basis of the curled state or the amount of curl detected by the curl sensor 201 as described above.

FIG. 16 is a flowchart showing an example of the control of the discharge speed of the sheet and the position of the movable tray 11, which is conducted by the control unit 204.

If the sheet is not upward or downward curled (no in Act 1), a predetermined standard discharge speed is maintained (Act 2). Also, as illustrated in FIG. 17A, a predetermined standard height difference H₁ is maintained (Act 3). In the present specification, the height difference is directed to a difference between a position of the discharge port 13 for the sheet, more particularly a position of an upper surface of the transport rollers 36 at the discharge port 13, and a position of the uppermost sheet stacked on the movable tray 11.

On the other hand, if the sheet is curled (yes in Act 1), and downward curled (yes in Act 2), the discharge speed is set to be lower than the standard discharge speed (Act 5). Also, as illustrated in FIG. 17B, the height level is set to a height difference H₂ smaller than the standard height difference H₁ (Act 6).

When the discharge speed is made low, the sheet can be prevented from dropping beyond the curved front portion of the stacked downward curled sheet. Also, when the height difference is reduced, the front end of the discharged sheet is abutted against a front side of the curved portion of the downward curled sheet, without the front end of the discharged sheet passing over the curved portion. Therefore, the sheet also can be prevented from dropping beyond the curved front portion of the sheet.

The height difference is determined according to the position of the uppermost sheet stacked on the movable tray 11 and the vertical position of the movable tray 11. The position of the uppermost sheet can be detected by the sheet height sensor 132 (refer to FIGS. 10 and 14), and the position of the movable tray 11 can be detected by a movable tray position sensor 111 (refer to FIGS. 11 and 14). With use of the above detection information, the height difference can be arbitrarily changed and set within a given range.

On the other hand, if the sheet is curled (yes in Act 1) and upward curled (no in Act 2), the discharge speed is set to be higher than the standard discharge speed (Act 6). The height difference is set to a height difference H₃ smaller than the standard height difference H₁ as in the case of the downward curl, as illustrated in FIG. 18B (FIG. 18A is identical with FIG. 17A) (Act 8). When the discharge speed increases, the sheet can advance against the wall of the curved front portion of the stacked downward curled sheet, thereby preventing the buckling or the rear end residual of the sheet caused by hitting the wall. Also, when the height difference is reduced, a distance by which the discharged sheet drops on the uppermost stacked sheet becomes also short. Therefore, the buckling phenomenon of the sheet can be prevented from occurring as well.

Incidentally, when the sheet is downward curled, the control unit 204 may set the discharge speed to be lower than the standard discharge speed by a speed proportional to the amount of downward curl, and when the sheet is upward curled, the control unit 204 may set the discharge speed to be higher than the standard discharge speed by a speed proportional to the amount of upward curl.

In addition, when the sheet is downward or upward curled, the control unit 204 may set the height difference between a highest position of the sheets stacked on the movable tray and a position of the discharge port to be smaller than a standard height difference when the sheet is not curled by an amount proportional to the amount of curl.

(3) Operation on Curled Sheet (Second Embodiment)

In the above-mentioned first embodiment, the position of the movable tray 11 is controlled by using the above-mentioned height difference. In contrast to this, in a second embodiment, a maximum stack amount is used to control the position of the movable tray 11. The movable tray 11 moves down with an increase in the number of stacked sheets, but a lower limit position is set. When the movable tray 11 arrives at the lower limit position, the movable tray 11 does not further move downward, and stops at that position. Even after the movable tray 11 has reached the stop position, the discharge of the sheet continues. Then, if the uppermost stacked sheet is abutted against the sheet height sensor 132, the discharge of the sheet stops. Accordingly, the number of sheets that can be stacked between a position of the stacked surface at the lower limit position of the movable tray 11 and a position of the sheet height sensor 132 becomes a maximum stack amount of the sheets (the maximum number of stacked sheets).

In the second embodiment, the maximum stack amount is controlled according to the curled state of the sheets. FIG. 19 is a flowchart showing an example of the control of the position of the movable tray 11 of the sheet, which is conducted by the control unit 204 in the sheet finishing apparatus 1 according to the second embodiment.

In an initial state, assuming that the sheet is not curled, a standard maximum stack amount A_(s) is set as illustrated in FIG. 20A.

If the downward curled sheet is detected by the curl sensor 201 (yes in Act 11), and a given number (X) of downward curled sheets are consecutively detected (yes in Act 12), as illustrated in FIG. 20B, the maximum stack amount is updated to a maximum stack amount A₂ smaller than the maximum stack amount set at that time (Act 13). For example, the maximum stack amount A₂ is set to be smaller than the set maximum stack amount by X sheets. If the maximum stack amount is not changed from an initial value, the maximum stack amount A₂ is set to a value smaller than the standard maximum stack amount A₅ by X sheets. Thereafter, if the upward curled sheet is not detected (no in Act 14), processing is advanced to determination in Act 17. The movable tray 11 moves down according to the number of stacked sheets, but does not move down to a position lower than the lower limit position corresponding to the maximum stack amount A₂. Accordingly, when the uppermost stacked sheet is abutted against the sheet height sensor 132, it is determined that the number of stacked sheets arrives at the maximum stack amount A₂ (yes in Act 17), and the discharge of the sheet stops (Act 18).

When the downward curled sheets are consecutively discharged, as illustrated in FIG. 20B, a curved portion is formed on the front end of each stacked sheet. In this situation, when the set maximum stack amount is large, there is a possibility that the discharged sheet drops under the movable tray 11 beyond the curved portion. To deal with this problem, in the sheet finishing apparatus 1 according to the second embodiment, when the downward curled sheets are consecutively discharged, the maximum stack amount is updated to be smaller than the maximum stack amount set at that time. As a result, the discharged sheets do not move beyond the curved front portion, and can prevent from dropping.

On the other hand, when the upward curled sheets are consecutively discharged, a wall can be formed in the front portion of the stacked sheets. For that reason, the newly discharged sheet abuts against the wall, resulting in that not only the above-mentioned sheet buckling phenomenon (FIG. 13B) but also the rear end residual of the sheets as illustrated in FIG. 21 occurs.

If the downward curled sheets are not detected (no in Act 11 of FIG. 19), and a given number (Y) of upward curled sheets are consecutively detected (yes in Act 14, yes in Act 15), as illustrated in FIG. 22B, the stack amount is updated to a maximum stack amount A₃ larger than the maximum stack amount set at that time (Act 16). For example, the maximum stack amount A₃ is set to be larger than the set maximum stack amount by Y sheets. If the maximum stack amount does not change from the initial value, the maximum stack amount A₃ is set to a value larger than the standard maximum stack A_(s) amount by Y sheets. When the maximum stack amount A₃ is set to be larger, a drop of the discharged sheet becomes larger, and the rear end residual of the sheet can be prevented.

(4) Discharge Speed Control Using Stacked Sheet Condition (Third Embodiment)

Conventionally, the control of the discharge speed using a condition in which the sheet is stacked on the movable tray 11 has not been conducted.

FIGS. 23A, 23C, and 23E are diagrams schematically illustrating the sheet stacked condition. If the discharge speed of the sheets is appropriate, as illustrated in FIG. 23A, the rear ends of most all sheets are abutted against the outer surfaces of the shutter 41 and the outer wall 20, and stops, and the sheets are stacked in a condition where the sheets are excellently aligned.

However, if the discharge speed of the discharged sheets is too high, and a flying distance is too long, as illustrated in FIG. 23C, the rear ends of the sheets do not return to the outer surface of the shutter 41 or the outer wall 20 due to a friction between the adjacent sheets, and becomes in a stacked condition where the alignment property is low.

On the other hand, if the discharge speed of the discharged sheets is too low, and a flying distance is too short, the rear ends of the sheets do not reach the outside of the shutter 41 or the outer wall 20, and the rear end residual phenomenon illustrated in FIG. 23E occurs.

In the sheet finishing apparatus 1 according to the third embodiment, the stacked condition of the sheets stacked on the movable tray 11 is detected by the sensor, and the discharge speed of the sheets is controlled by using the detected stacked condition.

As described above, the sheet height sensor 132 is disposed on the upper portion of the shutter 41. When a given number of sheets are discharged, the movable tray 11 moves upward, and the uppermost stacked sheet contacts the sheet height sensor 132. With detection of the contact position, the position of the uppermost sheet stacked on the movable tray 11 is detected. Thereafter, the movable tray 11 moves down by a given amount to receive the discharged sheets. In the third embodiment, the stacked condition of the sheets is detected using the on-state or off-state of the sheet height sensor 132.

In general, even if the discharge speed of the sheets is appropriate, and the alignment condition is excellent, a rear end surface of the stacked sheets is not a complete plane. Therefore, while the movable tray 11 moves vertically for a given detection period, the rear end surface of the sheets contact with the sheet height sensor 132, and thus, the sheet height sensor 132 generates a on-state and off-state at some frequency, as illustrated in FIG. 23B.

In the third embodiment, a standard frequency of the on-state and the off-state of the sheet height sensor 132 in the given detection period is measured and stored in advance as a reference value. The standard frequency is measured when the discharge speed of the sheets is set to be appropriate, i.e., is set to the standard discharge speed such that the alignment condition becomes excellent. During operation, the frequency of the on-state and the off-state of the sheet height sensor 132 is measured in the same detection period, and the stacked sheet condition is determined by comparing the measured frequency with the stored reference value.

FIG. 24 is a flowchart showing a processing example of the sheet discharge speed control in the sheet finishing apparatus 1 according to the third embodiment.

When the sheet is discharged (Act 20), it is determined whether a given number of sheets is discharged, or not (Act 21). When the number of sheets does not arrive at the given number, processing waits for subsequent discharge (Act 28, Act 20).

When the number of sheets arrives at the given number, in order to detect the height of the sheets, the movable tray 11 moves up to bring the rear end side of the sheets stacked on the upper portion thereof in contact with the sheet height sensor 132. Thereafter, the movable tray 11 moves down to a given position (Act 22).

Then, the number of turn-on in a given detection period after the sheet height sensor 132 first detects the sheets is counted (Act 23), and the number of turn-on is compared with a reference value (Act 24).

When the number of turn-on is substantially equal to the reference value, it is determined that the flying distance is normal, and the discharge speed of the sheets is maintained at the standard discharge speed.

On the other hand, when the flying distance is long, as illustrated in FIG. 23D, the frequency of turn-on becomes small. Accordingly, if the number of turn-on is smaller than the reference value, it is determined that the flying distance is too long, and the sheet discharge speed is made lower than the standard speed (Act 26).

On the other hand, if the flying distance is short, the frequency of turn-on becomes high, or the on-state is continued due to the rear end residual of the sheets as illustrated in FIG. 23F. Accordingly, if the number of turn-on is larger than the reference value, or if the on-state is continued for a given period, it is determined that the flying distance is too short, and the discharge speed of the sheet is made higher than the standard speed (Act 27).

According to the sheet finishing apparatus 1 of the third embodiment, because it is possible to detect the stacked condition of the sheets on the movable tray 11 by the aid of the existing sheet height sensor 132 without provision of an additional sensor, the costs are reduced. Also, because the discharge speed is controlled according to the sheet stacked condition, the alignment property of the sheets stacked on the movable tray 11 can be enhanced.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel apparatuses and units described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatuses and units described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention. 

1. A sheet finishing apparatus comprising: an outer wall having a discharge port of sheets; a movable tray on which the sheets discharged from the discharge port are stacked, the movable tray vertically moving along the outer wall according to a stack amount of the sheets; a curl sensor that detects a curled state of the sheets before the sheets are discharged from the discharge port; and a control unit that controls at least one of a discharge speed of the sheets and a position of the movable tray according to the detected curled state of the sheets.
 2. The device according to claim 1, wherein the curl sensor detects whether the sheet is in a downward curled state in which both ends or one end of the sheet is downward curved, an upward curled state in which both ends or one end of the sheet is upward curved, or a state in which the sheet is not curled.
 3. The device according to claim 2, wherein the curl sensor further detects the amount of upward or downward curl.
 4. The device according to claim 2, wherein when the sheet is downward curled, the control unit sets a discharge speed to be lower than a standard discharge speed when the sheet is not curled, and when the sheet is upward curled, the control unit sets the discharge speed to be higher than the standard discharge speed.
 5. The device according to claim 3, wherein when the sheet is downward curled, the control unit sets a discharge speed to be lower than the standard discharge speed by a speed proportional to the amount of downward curl, and when the sheet is upward curled, the control unit sets the discharge speed to be higher than the standard discharge speed by a speed proportional to the amount of upward curl.
 6. The device according to claim 2, wherein when the sheet is downward or upward curled, the control unit sets a height difference between a highest position of the sheets stacked on the movable tray and a position of the discharge port to be smaller than a standard height difference when the sheet is not curled.
 7. The device according to claim 3, wherein when the sheet is downward or upward curled, the control unit sets a height difference between a highest position of the sheets stacked on the movable tray and a position of the discharge port to be smaller than a standard height difference when the sheet is not curled by an amount proportional to the amount of curl.
 8. The device according to claim 1, wherein the curl sensor is a reflective optical sensor disposed on a transport path through which the sheets pass before being discharged from the discharge port, and detects that the sheets are downward curled, upward curled, or not curled, from a pattern of a change in reflection intensity with time while the sheets pass through the transport path.
 9. The device according to claim 2, wherein when a given number of downward curled sheets are consecutively discharged, the control unit sets a maximum stack amount of the movable tray to be smaller than a maximum stack amount set at that time, and when a total number of sheets stacked on the movable tray arrives at the set maximum stack amount, the control unit stops the discharge of the sheets.
 10. The device according to claim 2, wherein when a given number of upward curled sheets are consecutively discharged, the control unit sets a maximum stack amount of the movable tray to be larger than a maximum stack amount set at that time, and when a total number of sheets stacked on the movable tray arrives at the set maximum stack amount, the control unit stops the discharge of the sheets.
 11. A sheet finishing method comprising: providing an outer wall having a discharge port of sheets; vertically moving a movable tray on which the sheets discharged from the discharge port are stacked, along the outer wall having the discharge port according to a stack amount of the sheets; detecting a curled state of the sheets before the sheets are discharged from the discharge port by a curl sensor; and controlling at least one of a discharge speed of the sheets and a position of the movable tray according to the curled state of the sheets, which is detected by the curl sensor.
 12. The method according to claim 11, wherein whether the sheet is in a downward curled state in which both ends or one end of the sheet is downward curved, an upward curled state in which both ends or one end of the sheet is upward curved, or a state in which the sheet is not curled, is detected by the curl sensor.
 13. The method according to claim 12, further comprising: detecting the amount of upward or downward curl by the curl sensor.
 14. The method according to claim 12, wherein when the sheet is downward curled, a discharge speed is set to be lower than a standard discharge speed when the sheet is not curled, and when the sheet is upward curled, the discharge speed is set to be higher than the standard discharge speed.
 15. The method according to claim 13, wherein when the sheet is downward curled, a discharge speed is set to be lower than the standard discharge speed by a speed proportional to the amount of downward curl, and when the sheet is upward curled, the discharge speed is set to be higher than the standard discharge speed by a speed proportional to the amount of upward curl.
 16. The method according to claim 12, wherein when the sheet is downward or upward curled, a height difference between a highest position of the sheets stacked on the movable tray and a position of the discharge port is set to be smaller than a standard height difference when the sheet is not curled.
 17. The method according to claim 13, wherein when the sheet is downward or upward curled, a height difference between a highest position of the sheets stacked on the movable tray and a position of the discharge port is set to be smaller than a standard height difference when the sheet is not curled by an amount proportional to the amount of curl.
 18. The method according to claim 11, wherein the curl sensor is a reflective optical sensor disposed on a transport path through which the sheets pass before being discharged from the discharge port, and detects that the sheets are downward curled, upward curled, or not curled, from a pattern of a change in reflection intensity with time while the sheets pass through the transport path.
 19. The method according to claim 12, wherein when a given number of downward curled sheets are consecutively discharged, a maximum stack amount of the movable tray is set to be smaller than a maximum stack amount set at that time, and when a total number of sheets stacked on the movable tray arrives at the set maximum stack amount, the discharge of the sheets stops.
 20. The method according to claim 12, wherein when a given number of upward curled sheets are consecutively discharged, a maximum stack amount of the movable tray is set to be larger than a maximum stack amount set at that time, and when a total number of sheets stacked on the movable tray arrives at the set maximum stack amount, the discharge of the sheets stops. 